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Getting to the Heart of Chicken Ailments

Baby chicks are being bred for resistance to ascites, a fatal disease resulting
in heart failure in chickens. (K3627-16)

Humans aren't the only ones who
are susceptible to congestive heart failurethe heart's inability to
maintain adequate blood flow to tissues. Chickens, particularly broilers, fall
prey to a similar condition called ascites.

In chickens, the right ventricle of the heart enlarges and can't pump blood
efficiently to the lungs. Blood pressure then builds in the liver, and a yellow
serumlike fluid leaks from the liver into the body cavity, eventually leading
to death.

The problem has been around for about 20 years in birds grown at high
altitudes. But in the last decade, it has become a problem everywhere.

"Birds are genetically selected for fast growth. It now takes less than
6 weeks for birds to get to market," says poultry physiologist Janice M.
Balog. "Their hearts and lungs have to work harder to keep up with the
rapid rate of growth, and they just can't do it."

"Many factors, such as ammonia, dust, or respiratory
diseasescombined with accelerated growth rateshave led to a growing
problem among poultry producers," she says.

Balog, who is in the ARS Poultry
Production and Products Safety Research Unit in Fayetteville, Arkansas, has
made recent strides to prevent this fatal condition in poultry.

In an 8- by 12-foot room that holds 480 chickens, Balog's birds are taking a
trip to higher elevations. This room, called a hypobaric chamber, simulates
conditions found at higher altitudes. At a simulated 9,500 feet above sea
level, 80 to 90 percent of commercial broilers will develop ascites.

Using the hypobaric chamber allows Balog to identify and selectively breed
resistant birds and to test for possible remedies. In the fourth year of her
study, Balog and University of Arkansas poultry geneticist Nicholas Anthony,
have selected over four generations of broilers that have escaped this disease.
One population exhibits no more than 20 percent ascites at simulated high
altitudes.

"Once we are satisfied with the selected populations, we will attempt
to determine what's different physiologically between the two lines," says
Balog. "Ultimately, we hope to eliminate the disease."

Ascites research is particularly important because some birds die as early
as 3 weeks old, and more die before making it to processingafter the
producer has wasted a lot of money on feed costs that are passed on to the
consumer. Finding new ways to prevent this disease will reduce the amount of
money spent on birds that never make it to market.

Aside from genetic selection, Balog has found other ways poultry producers
can reduce the incidence of ascites, including increasing ventilation in
poultry houses and maintaining stable temperatures. Currently, producers
restrict the amount of feeda process that slows growth and reduces
mortalitybut birds on restricted diets take longer to reach market weight
and can have less white meatthe most valuable part of the chicken.

"We're looking at restricting feed during certain time periods. This
seems to help the problem," says Balog.By
Tara Weaver-Missick,
Agricultural Research Service Information Staff.